1. Field of the Invention
This invention relates to a sliver weight unevenness correcting apparatus, and more particularly, to an apparatus for accurately correcting silver weight unevenness, i.e. short in wavelength, suitable for use in recent high-speed spinning machines such as a drawing frame, a card and a comber.
2. Description of the Prior Art
In a drawing frame, a plurality of slivers fed from respective cans, which have been produced by carding machines in a previous process, are bundled and drafted together to eliminate the individuality of each sliver and to promote paralleling of the fibers. A drawing frame is known in the art, in which during the drafting operation, the draft of a draft device (hereinafter called a main draft device) of the drawing frame body is varied in response to the variations in weight per unit length of the slivers, thereby to correct the sliver weight unevenness. However, the conventional drawing frame is still disadvantageous in the following points: Since the slivers are run at high speed, correction of sliver weight unevenness by controlling the speed of the main draft device requires considerably high technique. In addition, the provision of the sliver weight unevenness correcting apparatus in the drawing frame body makes the construction intricate with the result that the size is necessarily increased.
In view of the difficulty accompanying the method in which the sliver weight unevenness is corrected in the drawing frame body, a method is known in the art, in which a sliver weight unevenness correcting apparatus is provided between the creel device and the drawing frame body with a main draft device in order to correct the weight unevenness before the slivers are introduced into the drawing frame body. However, the conventional method belongs to a so-called "feed-back system". Accordingly, the method reveals serious difficulties when employed for a recent high-speed drawing frame. In the feed-back system, the weight of slivers is measured after the slivers have passed through a correcting draft device, and therefore, time delay occurs before the unevenness correction is actually effected in the device after the weight measurement. Thus, in the system control according to the detected sliver weight (sliver weight unevenness correction) is made for the upstream slivers whose conditions are unknown. Therefore, the system suffers from the essential problem that it is impossible to perform the sliver weight unevenness correction with high accuracy. In the system, it is difficult to correct weight unevenness short in wavelength. The difficulty is further increased as the running speed of the slivers is increased. The above-described time delay is unavoidable because it is the sum of a signal transmission delay and a mechanical transmission delay. In the main draft device, the slivers are drafted four to nine times, and therefore the unevenness short in wavelength which has not been corrected will be increased four to nine times in length. Thus, the correction of the unevenness short in wavelength is the essential factor to determine the quality of produced slivers.
Mechanical means for measuring the sliver weight is generally of a type in which a bundle of slivers are collected and pressed to eliminate the air contained therein, whereby the total thickness of the pressed slivers is taken as the displacement of the depressing roller. Namely, in this case, the weight is substituted by the thickness. In this connection, in the feed-back system, the width of the bundle of slivers is increased to a predetermined value prior to passing through a sliver weight unevenness correcting draft device comprising variable speed draft rollers, so as to effect suitable drafting of the slivers, and then such slivers are to be collected or condensed for measuring in the sliver weight measuring section. Accordingly, the distance between the correcting draft device and the measuring section must be sufficiently long in order to effectively collect the slivers. If the sliver running speed is increased, then it is necessary to increase the distance, which further increases the deviation of unevenness detection. This makes it more difficult to correct the weight unevenness short in wavelength.
Furthermore, when the bundle of slivers passed through the measuring section is introduced into the main draft device, it is necessary to expand the collected slivers so that they are suitable for the main draft operation. Therefore, the distance between the sliver weight measuring section and the main draft device must also be considerably long. In other words, in order that the slivers may be greatly drafted in the main draft device, the slivers should be arranged in parallel with a suitable width and the long distance is required for smoothly and reqularly paralleling the bundle of slivers again which have once been collected. The distance is further increased as the sliver running speed is increased.
Thus, with the conventional device, it is necessary to provide a considerably long distance between the sliver weight unevenness correcting device and the main draft device, which results in the formation of a useless wide space. Another disadvantage is that it is impossible to correct the sliver weight unevenness short in wavelength.
Moreover, since a plurality of slivers are fed by feeding rollers of the creel device rotating at a constant speed, the tension of the slivers is always varied between the feeding rollers and the back rollers of the correcting draft device rotating at a variable speed, which results in irregular drafting.
There is still another difficulty in the correcting draft device when it is driven by an independent motor. Namely, in case the back rollers of the correcting draft device are connected to a variable speed rotation transmission mechanism driven by an independent motor to vary the speed of back rollers (relative to that of front rollers) through the transmission mechanism based on the instruction from the weight measurement section, the slivers are liable to be subjected to troubles during the starting, interrupting and inching operations of the apparatus. In this case, the instruction for varying the speed of back rollers is determined relative to the speed of the front rollers and then transmitted to the back rollers. In other words, the back rollers are rotated following the rotation of the front rollers. However, in the starting, interrupting and inching operations, the number of revolutions of the front rollers (i.e. the drawing frame body) is varied rapidly as compared with the response of the back rollers to the speed change instruction given thereto. As a result, during the starting operation, the back rollers may fail to sufficiently follow the front rollers so that the drafting ratio becomes so excessive as to sever the slivers. During the interrupting operation, the slivers are liable to be slackened between the front and back rollers thereby to make it difficult to effect the normal sliver forwarding operation. In addition, the inertial difference in the driving system of the front and back rollers exerts an influence to cause adverse affects upon the aforementioned slivers.
With respect to carding machines, a method is known in the art in which produced slivers are introduced from the doffer to the correcting draft device and to the sliver weight measuring section to correct the sliver weight uneveness. In this case also, if the weight unevenness correcting apparatus according to the feed-back system is employed for slivers which run at high speed, then the same troubles are caused, and particularly, it is extremely difficult to correct the unevenness short in wavelength. Other troubles will also occur as in a conventional drawing frame.